Battle Properties

Here are the Type Match-Ups for the Light type.

Only read on if you want my dull justification! (you were warned!)

Reasoning:
Light is strong vs Dark - because light dispels dark
.......................vs Bug - many bugs seek darkness, burning ants with magnifying glass, they get drawn to lights and often die etc...
.......................vs Electric - because UV light causes objects to lose electrical charge

Light is resisted by Grass - because they absorb light
..........................by Ghost - because they create and cast shadows / which in doing so means they absorb light
..........................by Light - because Light types are "used to it", in the same way fire resists fire and water resists water
..........................by Fairy - because, with attacks like Moonblast, there seems to be an element of light to this type, and so as above they are used to it.
..........................by Steel and Ice - because they are very reflective

Light is weak to Grass and Ghost - because they absorb light

Light resists Electric, Fire and Light - because they all produce light
Light resists Fairy- because again of the types' similarity and so they're used to it.

Dark does not affect Light - because obvious.

I have eliminated its relationship with Psychic as 7 resistances is too many, and technically flashes could distract the mind, thus be effective against Psychic types. Until more information on the Fairy type is revealed, this is how things stand.

Balance:
I believe these choices also wouldn't swing the gameplay too drastically. This is because the type itself is balanced. It has 8 good things (strong vs + resists + immunities) and 8 bad things (weak to + weak against). Moreover, the Grass type improves from this, and that is fine, as it is the worst type in terms for battle properties. The Ghost type also improves and Dark goes down. I feel this is fair, not only cos I love them, but because they got trumped by Dark types so badly. Both are super effective against Ghost and Psychic. But Dark resists one and is immune to the other, while Ghost is neutral for one, and weak to the other. So, why use a Ghost. Moreover, Ghost and Psychic Pokemon tend to have higher Special Defense than Defense, and Dark Pokemon have high Attack and an abundance of Physical moves, whereas Ghosts tend to have High Special Attack and Special moves. So again Dark is better. Dark Pokemon have overall higher average stats than ghosts too. So, rant over, but Ghost also deserved a boost in my opinion. Few other points, Ice previously only resisted itself, so this helps it a little. Steel resists so many things, this won't make much of a difference. And Finally, it was silly that Electric was only weak to one type, and quite a few could learn Grass Knot to take down Ground types. I know, Grass Knot would still be "super-effective" against Light types, but it would be nice to have moves other than Earthquake to target Electric types with. Fairy remains even, as the Light <--> Fairy relationship is mutual. Fire goes down a tiny bit. eh. and Bug goes down a bit too. Feel bad for that one, but they are like the first ones you catch!

Anyway, that's why I think these could be used as the match-ups for Light. And they result in the Light type being more of a defensive than offensive type, which I think suits it. I know many may not agree, and I'm happy to hear what you think. But when I created my Fakemon I had these in mind, so I'm unlikely to modify them. But do discuss your thoughts if you have any. Obviously no-one can be right or wrong on something like this, so just interesting to know what people think!

Enjoy!